The present application relates to counterweight blocks and associated assemblies; mobile lift cranes using the counterweight blocks to provide counterweight to its loads; and methods of making and utilizing the counterweight blocks and associated assemblies.
Mobile lift cranes such as the one referred to herein are very heavy and must be broken down into pieces for transportation between job sites, wherein the weight of each piece that is transported must be within highway transportation weight limits. The allowable weight limit of each piece may vary in some countries, and may also vary based on the weight of the transportation vehicles. Accordingly, it is necessary to build the crane in a modular way, keeping each piece within at least the weight limits of the largest transportable load.
In the United States, the maximum weight that may be placed on a trailer for long haul transportation, without a special permit, is 44,000 pounds, or 20 metric tonne. Typical counterweight blocks each weigh 10 metric tonne. While the counterweight blocks could be transported in a stacked configuration on a flat bed, typically two counterweight blocks are placed one over each axel of the flat bed to spread the load out. Some countries also have maximum width limitations. In addition to transportability, customer needs, and supplier or foundry availability affect design of counterweight blocks, which are typically cast or built in weights of 5, 10, or 20 metric tonne.
A crane at a job site lifts very heavy loads, and therefore, requires a substantial number of the counterweight blocks on a counterweight tray of the crane to provide a counterweight for lifting those loads. The heavier the load, the more counterweight blocks that are needed on the counterweight tray, which means that the counterweight blocks are often stacked together. Since some cranes use hundreds of metric tonne of counterweight blocks, it can take a long time to transport and stack the counterweight blocks at the job site. Additionally, it can be difficult to keep higher stacks of counterweight blocks secured to prevent them from tipping while the crane is in operation, especially if the stack is moveable with respect to the rest of a rotating bed of the crane.